The disclosure relates to linear gages. More particularly, the disclosure relates to alignment adjustment in linear gages.
A linear gage is known as a small-size precision measuring instrument (See Japanese Patent Publication No. H8-27161B, Japanese Patent No. 2557171B, Japanese Unexamined Patent Application Publication No. 2007-322248A, Japanese Unexamined Patent Application Publication No. 2015-75397A and Japanese Unexamined Patent Application Publication No. 2016-14534A, for example). (Note that names such as digital dial gage, electronic micrometer, Digimatic indicator (“Digimatic” is a trademark), linear gage, and the like are also used.)
A linear gage measures a workpiece with an extremely high level of precision by using a digital encoder to precisely detect displacement in the axial direction of a spindle.
FIG. 1 schematically illustrates the inner mechanism of a linear gage.
In FIG. 1, a spindle 110 is a cylindrical rod that is guided to move forward and rearward by a bushing 10. A pin 112 is inserted into a side surface of the spindle 110 to prevent the spindle 110 from rotating, and a guide slit 11 is formed in the bushing 10. The guide slit 11 is formed such that the pin 112 can be passed therethrough, and the guide slit 11 is longer in the axial direction. The guide slit 11 guides the pin 112 such that the spindle 110 can move forward and rearward in the axial direction but is restricted from rotating around the longitudinal axis of the gage, which extends in the axial direction.
An encoder 300 is provided at a rear end side of the spindle 110. The encoder 300 is constituted of a scale 310 and a detection head 320. The scale 310 is fixed to the rear end of the spindle 110, and the detection head 320 is disposed opposite the scale 310 with a predetermined gap provided therebetween.
The measuring accuracy of a linear gage depends on the processing accuracy (the manufacturing accuracy) of the components and the detection accuracy of the encoder 300.
In terms of the processing accuracy of the components, it is extremely important that the spindle moves straight, for example. Thus, effort is made to increase the straightness of the spindle 110 itself, as well as the processing accuracy of the inner surface of the bushing 10, to the greatest extent possible. Meanwhile, to increase the detection accuracy of the encoder 300, it is necessary for the scale 310 and the detection head 320 to be kept parallel across the entire measurement stroke. If the spindle 110 rotates around the axis even slightly, the relative attitudes of the scale 310 and the detection head 320 will shift, which destabilizes the detection accuracy by that amount. As such, effort is made to finish the outer diameter of the pin 112 and the width of the guide slit 11 with a high level of precision, such that there is no looseness (gap, play) between the pin 112 and the guide slit 11.